Evinrude and Johnson 7.5 and 10 hp [1955-1963] fuel / oil ratios

SPK

Seaman
Joined
Nov 21, 2010
Messages
55
Hello,
I recently came across a good resource book to share with members of the forum. It is called "Old Outboard Motor" service manual volume 1. The publisher is Intertec and it covers motors below 30 hp prior to 1969. I found it through my local library.
In the section devoted to Evinrude and Johnson, 7.5 an 10 hp from the years 1955 to 1963 the fuel/oil ratio is as follows;

7.5 Evinrude and Johnson, 16:1, 1/2 pint to a galllon of unleaded gasoline


10 Evinrude and Johnson, 24:1, 1/3 pint to a gallon of unleaded gasoline.

This information was found on page 184 of this manual.

I don't own an owner's manual for my 7.5 hp Johnson[1958] but if someone out there does perhaps they could verify or dispute the information I have found.
I really enjoy reading the forums and would appreciate any feedback with respect to the above topic.
Thanks so much.
SPK.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: Evinrude and Johnson 7.5 and 10 hp [1955-1963] fuel / oil ratios

That is correct, per the factory service manual.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Evinrude and Johnson 7.5 and 10 hp [1955-1963] fuel / oil ratios

Depends on which Factory Service Manual you look in. My 1964 edition of the Johnson Outboard Service Manual calls for 24:1 in both of those outboards.

If I had your 7.5 I would probably run it on 24:1 with the original Champion J4C plugs, but that is my decision, my risk.

Risk is minimum running a more oil-rich mixture than actually needed, as long as you use the hotter-than-original Champion J6C plugs which are now pretty much universally suggested. If you are going to run 16:1 be sure to use the J6C and gap them at .035-040".

This discussion goes round and round regularly and all arguments are usually valid because each can quote an official document.

A really conservative point of view is that outboards need oil like people need water. More than you need is okay; less than you need will kill you.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: Evinrude and Johnson 7.5 and 10 hp [1955-1963] fuel / oil ratios

I can show you a Johnson factory document saying both can be run on 50:1 Personally, I run all my older motors on 24:1. But that's my decision.
 

Tim Frank

Vice Admiral
Joined
Jul 29, 2008
Messages
5,333
Re: Evinrude and Johnson 7.5 and 10 hp [1955-1963] fuel / oil ratios

I suspect at least part of the ambiguity results from the huge advances in luricant quality. If you were using the oil that was available in the days when they rec'd 16:1....you would probably be best to use that ratio.
The new high-end TCW3 oils would probably be fine at 50:1 or even higher.
 
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